Table_3_Ice Nucleation Activity and Aeolian Dispersal Success in Airborne and Aquatic Microalgae.pdf

Microalgae are common members of the atmospheric microbial assemblages. Diverse airborne microorganisms are known to produce ice nucleation active (INA) compounds, which catalyze cloud and rain formation, and thus alter cloud properties and their own deposition patterns. While the role of INA bacteria and fungi in atmospheric processes receives considerable attention, the numerical abundance and the capacity for ice nucleation in atmospheric microalgae are understudied. We isolated 81 strains of airborne microalgae from snow samples and determined their taxonomy by sequencing their ITS markers, 18S rRNA genes or 23S rRNA genes. We studied ice nucleation activity of airborne isolates, using droplet freezing assays, and their ability to withstand freezing. For comparison, we investigated 32 strains of microalgae from a culture collection, which were isolated from polar and temperate aqueous habitats. We show that ∼17% of airborne isolates, which belonged to taxa Trebouxiphyceae, Chlorophyceae and Stramenopiles, were INA. A large fraction of INA strains (over 40%) had ice nucleation activity at temperatures ≥-6°C. We found that 50% of aquatic microalgae were INA, but the majority were active at temperatures <-12°C. Most INA compounds produced by microalgae were proteinaceous and associated with the cells. While there were no deleterious effects of freezing on the viability of airborne microalgae, some of the aquatic strains were killed by freezing. In addition, the effect of desiccation was investigated for the aquatic strains and was found to constitute a limiting factor for their atmospheric dispersal. In conclusion, airborne microalgae possess adaptations to atmospheric dispersal, in contrast to microalgae isolated from aquatic habitats. We found that widespread taxa of both airborne and aquatic microalgae were INA at warm, sub-zero temperatures (>-15°C) and may thus participate in cloud and precipitation formation.

微藻是大气微生物群落的常见组成类群。已知多种空气传播微生物可产生冰核活性（ice nucleation active, INA）物质，该类物质可催化云与降雨形成，进而改变云的物理属性及其自身的沉积模式。尽管冰核活性细菌与真菌在大气过程中的作用已受到广泛关注，但大气微藻的数量丰度及其冰核活性的相关研究仍有待深入。本研究从雪样中分离得到81株空气传播微藻，并通过测序ITS标记、18S核糖体RNA（rRNA）基因或23S rRNA基因对其进行分类鉴定。我们采用液滴冻结试验测定了空气分离株的冰核活性，并检测了其耐受冻结的能力。为进行对照研究，我们还分析了保藏于培养物保藏库的32株微藻，这些菌株分离自极地与温带的水生环境。研究显示，约17%的空气分离株隶属于共球藻纲（Trebouxiphyceae）、绿藻纲（Chlorophyceae）以及不等鞭毛类（Stramenopiles），均具有冰核活性。其中超过40%的冰核活性菌株可在≥-6℃的温度下发挥冰核作用。我们发现，50%的水生微藻具有冰核活性，但其中大多数仅在<-12℃的温度下才具备活性。微藻产生的绝大多数冰核物质为蛋白质类，且与细胞结合。冻结过程对空气传播微藻的存活率无不利影响，但部分水生菌株会因冻结而死亡。此外，我们针对水生菌株开展了干燥胁迫试验，结果表明干燥是限制其大气传播的关键因素。综上，与分离自水生环境的微藻相比，空气传播微藻具备适应大气传播的特性。我们发现，广泛分布的空气与水生微藻类群均可在>-15℃的亚零低温下表现出冰核活性，因此可能参与云形成与降水过程。